Light emitting diode and method of fabricating the same

ABSTRACT

Disclosed herein is a light emitting diode. The light emitting diode includes a support substrate, semiconductor layers formed on the support substrate, and a metal pattern located between the support substrate and the lower semiconductor layer. The semiconductor layers include an upper semiconductor layer of a first conductive type, an active layer, and a lower semiconductor layer of a second conductive type. The semiconductor layers are grown on a sacrificial substrate and the support substrate is homogeneous with the sacrificial substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/811,047, filed on Jun. 28, 2010, which is the National Stage ofInternational Application No. PCT/KR2008/007658, filed on Dec. 24, 2008,and claims priority from and the benefit of Korean Patent ApplicationNo. 10-2007-0140605, filed on Dec. 28, 2007, and Korean PatentApplication No. 10-2008-0131071, filed on Dec. 22, 2008, which are allhereby incorporated by reference for all purposes as if fully set forthherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting diode and a method offabricating the same, and more particularly, to a light emitting diodefabricated through a laser lift-off (LLO) process and a method offabricating the same.

2. Discussion of the Background

Typically, a light emitting diode (LED) is formed by growing a GaN-basedmaterial on a substrate formed of GaN, sapphire, silicon, siliconnitride, and the like to emit light. In the LED with this structure,light is emitted from a light emitting layer located at an upper portionof the LED, travels above and below the light emitting layer, and isfinally emitted from the LED through reflection, scattering, andrefraction. To increase luminescence efficiency through refraction andreflection of light traveling above and below the light emitting layer,it is necessary to form a roughness on an upper side of the lightemitting layer or to provide a reflection plate having good reflectivityto a lower side of the light emitting layer.

However, an upper side P-type layer of the light emitting layer is sothin that the roughness cannot be formed thereon or, if any roughness isformed thereon, provides an insignificant effect. Further, even when ametallic material having good reflectivity is deposited under thesapphire substrate located below the light emitting layer, some light isinevitably absorbed and disappears in the sapphire substrate. As such,when light is emitted from the lower part of the LED, it passes throughthe substrate where the light undergoes a significant loss. To reducesuch a loss, a Si substrate or a metal substrate is provided to the LEDfor preventing absorption of light in the substrate while improvingreflectivity, instead of using a sacrificial substrate, which hasconventionally been used to grow semiconductor layers for use in theformation of the roughness or in the deposition of metal having highreflectivity to the substrate.

When using heterogeneous substrates instead of the sacrificialsubstrate, it is necessary to form an intermediate layer to bond theheterogeneous substrates to each other through application of heat andpressure from above and below the intermediate layer. During theapplication of heat and pressure, the heterogeneous substrates undergodeformation due to a difference in thermal expansion coefficienttherebetween. Such deformation causes problems relating tocharacteristics and yield of subsequent processes.

SUMMARY OF THE INVENTION

The present invention is conceived to solve such problems of the relatedart as described above, and an aspect of the present invention is toprovide a light emitting diode and method of fabricating the same, whichcan solve the problems of the related art.

In accordance with an aspect of the present invention, a light emittingdiode includes a support substrate; semiconductor layers formed on thesupport substrate, the semiconductor layers including an uppersemiconductor layer of a first conductive type, an active layer, and alower semiconductor layer of a second conductive type; and a metalpattern located between the support substrate and the lowersemiconductor layer, the semiconductor layers being grown on asacrificial substrate and the support substrate being homogeneous withthe sacrificial substrate.

The support substrate may be a sapphire substrate.

The support substrate may be formed at an upper or lower portion thereofwith a plurality of grooves or through-holes filled with a metal.

The metal pattern may include a reflective metal layer on at least aportion of a lower surface of the lower semiconductor layer, and anintermediate metal layer covering the reflective metal layer.

The intermediate metal layer may include a protective metal layer.

The protective metal layer may be composed of multiple layers.

The intermediate metal layer may include a bonding metal layer.

The bonding metal layer may be composed of multiple layers.

The light emitting diode may further include an indium tin oxide (ITO)layer interposed between the lower semiconductor layer and thereflective metal layer.

The metal pattern may include a reflective metal layer on a lowersurface of the lower semiconductor layer; and an intermediate metallayer between the reflective metal layer and the support substrate, thesemiconductor layers being located on at least a portion of thereflective metal layer.

The reflective metal layer may include DBR layers partially formedtherein.

The light emitting diode may further include electrode pads formed onthe upper semiconductor layer and the metal pattern, respectively.

In accordance with another aspect of the present invention, a lightemitting diode includes a support substrate; a plurality of metalpatterns spaced from each other on the support substrate; light emittingcells located on at least some regions of the respective metal patterns,each light emitting cell including an upper semiconductor layer of afirst conductive type, an active layer and a lower semiconductor layerof a second conductive type; metal wires electrically connecting uppersurfaces of the light emitting cells to the metal patterns adjacent tothe upper surfaces thereof, the semiconductor layers being grown on asacrificial substrate and the support substrate being homogeneous withthe sacrificial substrate.

The support substrate may be a sapphire substrate.

The support substrate may be formed at an upper or lower portion thereofwith a plurality of grooves or through-holes, the grooves orthrough-holes being filled with metal.

The metal pattern may include a reflective metal layer on at least aportion of a lower surface of the lower semiconductor layer; and anintermediate metal layer covering the reflective metal layer.

The intermediate metal layer may include a protective metal layer.

The protective metal layer may be composed of multiple layers.

The intermediate metal layer may include a bonding metal layer.

The bonding metal layer may be composed of multiple layers.

The light emitting diode may further include an indium tin oxide (ITO)layer between the lower semiconductor layer and the reflective metallayer.

The metal pattern may include a reflective metal layer on a lowersurface of the lower semiconductor layer; and an intermediate metallayer between the reflective metal layer and the support substrate, thesemiconductor layers being located on at least a portion of thereflective metal layer.

The reflective metal layer may include DBR layers partially formedtherein.

In accordance with a further aspect of the present invention, a methodof fabricating a light emitting diode includes: forming semiconductorlayers on a first substrate, the semiconductor layers including a bufferlayer, a first conductive semiconductor layer, an active layer and asecond conductive semiconductor layer; forming a metal pattern on thesecond conductive semiconductor layer; forming a second substrate on themetal pattern, the second substrate being homogeneous with the firstsubstrate; separating the first substrate from the semiconductor layers;patterning the semiconductor layers and the metal pattern to formseparated metal patterns and light emitting cells located on someregions of the respective separated metal patterns; and dicing thesecond substrate for each of the light emitting cells to provideindividual chips.

The first and second substrates may be sapphire substrates.

The forming a metal pattern may include forming reflective metal layersseparate from each other on the second conductive semiconductor layer;and forming an intermediate metal layer covering the second conductivesemiconductor layer and the reflective metal layers.

The method may further include forming a plurality of grooves orthrough-holes at an upper or lower portion of the second substrate, andforming metal layers in the grooves or the through-holes, before formingthe second substrate on the metal pattern.

In accordance with yet another aspect of the present invention, a methodof fabricating a light emitting diode includes: forming semiconductorlayers on a first substrate, the semiconductor layers including a bufferlayer, a first conductive semiconductor layer, an active layer and asecond conductive semiconductor layer; forming a metal pattern on thesecond conductive semiconductor layer; forming a second substrate on themetal pattern, the second substrate being homogeneous with the firstsubstrate; separating the first substrate from the semiconductor layers;patterning the semiconductor layers and the metal pattern to formseparated metal patterns and light emitting cells located on someregions of the respective separated metal patterns; and forming metalwires electrically connecting upper surfaces of the light emitting cellsto the metal patterns adjacent to the upper surfaces thereof.

The forming a metal pattern may include reflective metal layers separatefrom each other on the second conductive semiconductor layer; andforming an intermediate metal layer covering the second conductivesemiconductor layer and the reflective metal layers.

According to an embodiment of the present invention, the supportsubstrate is homogeneous with the sacrificial substrate. Thus, when thesemiconductor layers and the support substrate are subjected to abonding process at a high temperature and pressure, deformation of thesupport substrate can be effectively prevented after the bonding processat the high temperature and pressure since there is no difference inthermal expansion coefficient between the sacrificial substrate and thesupport substrate. As the support substrate is not deformed, an LLOprocess, an etching process or a polishing process can be carried outvery precisely and easily. As a result, the light emitting diode can beproduced at improved yield and with improved luminescencecharacteristics.

Further, according to an embodiment of the present invention, aplurality of metal layers are formed in the support substrate toeffectively emit heat from the light emitting diode, thereby allowingeffective manufacture of high power LEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a light emitting diode according toan embodiment of the present invention;

FIGS. 2 to 6 are cross-sectional views illustrating a method offabricating a light emitting diode according to an embodiment of thepresent invention;

FIGS. 7 and 8 are graphs depicting improved luminescence characteristicsof a light emitting diode according to an example of the presentinvention compared with those of comparative examples;

FIG. 9 is a cross-sectional view of a light emitting diode according toanother embodiment of the present invention;

FIGS. 10 to 12 are cross-sectional views of light emitting diodesaccording to other embodiments of the present invention;

FIG. 13 is a cross-sectional view of a light emitting diode according toyet another embodiment of the present invention;

FIG. 14 is a cross-sectional view of a light emitting diode according toyet another embodiment of the present invention;

FIGS. 15 to 20 are cross-sectional views illustrating a method offabricating the light emitting diode shown in FIG. 14; and

FIG. 21 is a cross-sectional view of a light emitting diode according toyet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings. The embodiments aregiven by way of illustration for full understanding of the presentinvention by those skilled in the art. Hence, the present invention isnot limited to these embodiments and can be realized in various forms.Further, for convenience of description, width, length, and thickness ofcomponents are not drawn to scale in the drawings. The same componentswill be denoted by the same reference numerals throughout thespecification.

FIG. 1 is a cross-sectional view of a light emitting diode according toan embodiment of the present invention.

Referring to FIG. 1, a metal pattern 40 is formed on a support substrate51. The support substrate 51 may comprise sapphire, AlN or GaN. Thesupport substrate 51 is homogeneous with a sacrificial substrate that isused for growing semiconductor layers constituting a light emitting cell30. In this embodiment, the support substrate 51 is a sapphire substrateserving as an insulation substrate.

The metal pattern 40 may include a reflective metal layer and/or anintermediate metal layer. Here, the intermediate metal layer is a metallayer interposed between the light emitting cell 30 and the supportsubstrate 51, and is functionally or regionally distinguished from thereflective metal layer when realized along with the reflective metallayer. However, when not including a separate reflective metal layer,the metal pattern 40 may be realized to have the function of thereflective metal layer. The intermediate metal layer may include aprotective metal layer. The protective metal layer can protect thereflective metal layer. The intermediate metal layer may include abonding metal layer for bonding the support substrate 51.

In this embodiment, the metal pattern 40 includes a reflective metallayer 31 a, a protective metal layer 32 a, a first bonding metal layer33 a, and a second bonding metal layer 53 a. However, the presentinvention is not limited to this configuration, and can be modified invarious forms.

The reflective metal layer 31 a is formed of a metallic material havinghigh reflectivity, for example, silver (Ag) or aluminum (Al). Theprotective metal layer 32 a is a diffusion preventing layer, whichprevents metal elements from being diffused into the reflective metallayer 31 a, and can maintain the reflectivity of the reflective metallayer 31 a. The protective metal layer 32 a may be a single layer ormultiple layers, and formed of, for example, Ni, Ti, Ta, Pt, W, Cr, Pd,or the like.

The first and second bonding metal layers 33 a and 53 a are provided forbonding the reflective metal layer 31 a and the support substrate 51,and each may be formed in a single layer or in multiple layers. Thefirst and second bonding metal layers 33 a and 53 a may be formed of Au,Sn or alloys of Au and Sn (for example, 80/20 wt % or 90/10 wt %). Here,in order to enhance contact characteristics, Cr/Au, Ni or Ti may befurther used. Additionally, the first and second bonding metal layers 33a and 53 a may be formed using In, Ag or Al.

The light emitting cell 30 is located on at least some regions of eachmetal pattern. The light emitting cell 30 includes a lower P-typesemiconductor layer 29 a, an active layer 27 a, and an upper N-typesemiconductor layer 25 a. The active layer 27 a is interposed betweenthe P-type semiconductor layer 29 a and the N-type semiconductor layer25 a, the locations of which can be changed.

The N-type semiconductor layer 25 a may be formed of N-typeAl_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1), and may include an N-type cladlayer. Further, the P-type semiconductor layer 29 a may be formed ofP-type Al_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1), and may include a P-typeclad layer. The N-type semiconductor layer 25 a may be formed by dopingsilicon (Si) and the P-type semiconductor layer 29 a may be formed bydoping zinc (Zn) or magnesium (Mg).

The active layer 27 a serves as a region where electrons and holes arecombined, and comprises InGaN. The wavelength of light emitted from thelight emitting cell is determined according to the kind of materialsconstituting the active layer 27 a. The active layer 27 a may bemultiple layers formed by alternately laminating a quantum well layerand a barrier layer. The quantum well layer and the barrier layer may bebinary to quaternary-compound semiconductor layers represented bygeneral formula Al_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1).

A metal wire 57 is formed to supply electric power to the metal pattern40, and a metal wire 59 is formed to supply electric power to the N-typesemiconductor layer 25 a. For this purpose, an electrode pad 55 may beformed on the N-type semiconductor layer 25 a. The electrode pad 55reduces contact resistance through ohmic contact with the N-typesemiconductor layer 25 a.

FIGS. 2 to 6 are cross-sectional views illustrating a method offabricating a light emitting diode according to an embodiment of thepresent invention.

Referring to FIG. 2, semiconductor layers including a buffer layer 23,an N-type semiconductor layer 25, an active layer 27 and a P-typesemiconductor layer 29 are formed on a first substrate 21, followed byforming a reflective metal layer 31 on the semiconductor layers.

Advantageously, the first substrate 21 is transparent like a sapphiresubstrate and is coherent to lattices of the semiconductor layers.

The buffer layer 23 and the semiconductor layers 25, 27 and 29 may beformed by metal organic chemical vapor deposition (MOCVD), molecularbeam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or the like.Further, the semiconductor layers 25, 27 and 29 may be consecutivelyformed in a single chamber.

The buffer layer 23 may be formed of a particular material so long as itcan release lattice mismatch between the first substrate 21 and thesemiconductor layers 25, 27 and 29. For example, the buffer layer 23 maybe formed of un-doped GaN.

The reflective metal layer 31 is formed of a metal, preferably, a metalwith high reflectivity, for example Ag or Al, which forms ohmic-contactwith the P-type semiconductor layer. Further, the reflective metal layeris preferably formed of a metal with a high heat transfer rate, forexample, Au or a laminate of Au and Sn. A protective metal layer 32 isformed on the reflective metal layer 31. The protective metal layer 32serves as a diffusion preventing layer. A first bonding metal layer 33is formed on the protective metal layer 32. The first bonding metallayer 33 is provided for metal bonding and is not limited to aparticular material. The first bonding metal layer 33 may be formed ofAu, Sn or alloys of Au and Sn (for example, 80/20 wt % or 90/10 wt %) ina single layer or multiple layers. Here, in order to enhance contactcharacteristics, Cr/Au, Ni or Ti may be further used. Additionally, thefirst bonding metal layer 33 a may be formed using In, Ag or Al.

A second bonding metal layer 53 is formed on a second substrate 51separate from the first substrate 21. The second substrate 51 ishomogeneous with the first substrate 21.

The second bonding metal layer 53 is provided for metal bonding with thefirst bonding metal layer 33, and is not limited to a particularmaterial. The second bonding metal layer 53 may be formed of Au, Sn oralloys of Au and Sn (for example, 80/20 wt % or 90/10 wt %) in a singlelayer or multiple layers. Here, in order to enhance contactcharacteristics, Cr/Au, Ni or Ti may be further used. Additionally, thesecond bonding metal layer 53 a may be formed using In, Ag or Al.

Referring to FIG. 3, the first bonding metal layer 33 and the secondbonding metal layer 53 are bonded to each other to face each other. Suchbonding can be easily performed through application of a predeterminedpressure and/or heat.

Then, a laser is irradiated from a side of the first substrate 21. Thelaser may be, for example, a KrF (248 nm) laser. Since the firstsubstrate 21 is a transparent substrate like a sapphire substrate, thelaser passes through the first substrate 21 and is absorbed by thebuffer layer 23. As a result, the buffer layer 23 is decomposed at aninterface between the buffer layer 23 and the first substrate 21 by theabsorbed radiation energy, so that the substrate 21 is separated fromthe semiconductor layers.

Referring to FIG. 4, after the first substrate 21 is separated from thesemiconductor layers, the remaining buffer layer 23 is removed to exposethe surface of the N-type semiconductor layer 25. The buffer layer 23can be removed by etching or polishing.

Referring to FIG. 5, the semiconductor layers 25, 27 and 29, and themetal layers 31, 32, 33 and 53 are patterned by photolithography oretching to form metal patterns separated from each other and a lightemitting cell 30 located on some regions of each metal pattern.

The light emitting cell 30 includes the P-type semiconductor layer 29 a,the active layer 27 a, and the N-type semiconductor layer 25 a, whichare subjected to the patterning process. The semiconductor layers 25 a,27 a and 29 a may be patterned to have identical shapes.

On the other hand, since the second substrate 51 is an insulationsubstrate and the metal patterns 40 are separated from each other, thelight emitting cells 30 are electrically isolated from each other.

Referring to FIG. 6, with the light emitting cells 30 electricallyisolated from each other, the second substrate 51 is divided intoindividual chips by dicing the second substrate 51 for the respectivelight emitting cells 30. Then, metal wires 57 and 59 are formed on therespective upper surfaces of the light emitting cells 30 and the metalpatterns 40 to supply electric power.

On the other hand, before forming the metal wires, an electrode pad 55may be formed on the N-type semiconductor layer 25 a. The electrode pad55 forms ohmic-contact with the N-type semiconductor layer 25 a. Here,although the metal wire 57 is shown as being connected to a right upperside of the metal pattern in the drawing, the metal wire 57 can beconnected to a left upper side thereof, as needed.

In this embodiment, since the metal pattern 40 is formed, it is possibleto eliminate a process of forming a separate electrode pad on the P-typesemiconductor layer 29 a.

According to this embodiment, the P-type semiconductor layer 29 and theN-type semiconductor layer 25 may be formed in a reverse order. In thiscase, a transparent electrode may be formed on the P-type semiconductorlayer 29 after removing the buffer layer 23.

FIGS. 7 and 8 are graphs depicting improved luminescence characteristicsof a light emitting diode according to an example of the presentinvention compared with those of comparative examples.

In the FIG. 7, example of the present invention is compared with thecomparative examples 1 to 4, and in the FIG. 8, example of the presentinvention is compared with the comparative example 1.

EXAMPLE

A light emitting diode fabricated by growing semiconductor layers on asacrificial substrate formed of sapphire, followed by using a sapphiresubstrate as a support substrate and separating the sacrificialsubstrate.

Comparative Example 1

A light emitting diode fabricated by growing semiconductor layers on asacrificial substrate formed of sapphire, followed by using thissubstrate without separation thereof.

Comparative Example 2

A light emitting diode fabricated by growing semiconductor layers on asacrificial substrate formed of sapphire, followed by using aSi-substrate as a support substrate and separating the sacrificialsubstrate.

Comparative Example 3

A light emitting diode fabricated by growing semiconductor layers on asacrificial substrate formed of sapphire, followed by using aCu-substrate as a support substrate and separating the sacrificialsubstrate.

Referring to FIG. 7, it can be seen that the light emitting diode of theExample exhibited improved relative light intensity with respect toinput current, as compared with those of Comparative Examples 1 to 3.

The substrate of Comparative Example 1 was the sapphire substrate, whichwas used as the support substrate in the Example. However, in the lightemitting diode of Comparative Example 1, the sapphire substrate used togrow the semiconductor layers was used without being separated.

On the other hand, in the light emitting diode of the Example, thesapphire substrate was used as the support substrate, thereby preventingdeformation of the semiconductor layers during manufacture of the lightemitting diode after separating the sapphire substrate used as thesacrificial substrate. Further, the light emitting diode of the Exampleincluded a metal pattern between the support substrate and thesemiconductor layers, thereby improving an effect of spreading electriccurrent.

In Comparative Example 2, after the semiconductor layers were grown onthe sacrificial substrate of sapphire, the Si-substrate was used as thesupport substrate. For Comparative Example 2, the relative lightintensity with respect to input current was most similar to that of theExample. However, the Si-substrate has a different thermal expansioncoefficient than the sacrificial substrate of sapphire. Thus, whenperforming a process of bonding the semiconductor layers to the supportsubstrate at high temperature and pressure, the semiconductor layers andsupport substrate are concavely deformed towards the sacrificialsubstrate. If the deformation of the semiconductor layers and supportsubstrate toward the sacrificial substrate occurs, precision of an LLOprocess, an etching process or a polishing process is deteriorated,thereby reducing yield of the light emitting diode. Further, thissubstrate is likely to be broken when the substrate is picked up andtransferred by a certain device during manufacture of the light emittingdiode.

Further, in Comparative Example 3, after the semiconductor layers weregrown on the sacrificial substrate of sapphire, the Cu-substrate wasused as the support substrate. However, since a metallic substrate suchas a Cu substrate is not rigid, the substrate is liable to deform whenthe substrate is picked up and transferred by a certain device duringmanufacture of the light emitting diode. On the contrary, the sapphiresubstrate used as the support substrate of the Example is not deformedwhen picked up and transferred by a certain device during manufacture ofthe light emitting diode.

Referring to FIG. 8, it can be seen that the light emitting diode of theExample exhibited improved wavelength shift (Wd shift) according toinput current, as compared with that of Comparative Example 1.

FIG. 9 is a cross-sectional view of a light emitting diode according toanother embodiment of the present invention.

Referring to FIG. 9, a Distribution Bragg Reflector (DBR) pattern 31 bis formed in a reflective metal layer 31 a. The DBR pattern 31 b adjoinsa lower surface of a P-type semiconductor layer 29 and is constituted byDBRs spaced from each other. The DBR pattern 31 b may be formed inmultiple layers by alternately laminating insulation layers havingdifferent indexes of refraction.

The DBR pattern 31 b is formed by alternately laminating two kinds ofmediums having different indexes of refraction, and can reflect lightbased on a difference in the indexes of refraction thereof. The DBRpattern 31 b allows effective scattering of light and compensates foroptical reflection of the reflective metal layer 31 a by primarilyreflecting light generated from the active layer 27 a through increasein reflectivity.

The DBR pattern 31 b may be formed by alternately laminating two or moreinsulation layers having different indexes of refraction. For example,the DBR pattern 31 b may be formed by alternately laminating an SiO₂layer and an Si₃N₄ layer in multiple layers. Referring to FIG. 1, aftersequentially forming an N-type semiconductor layer 27, an active layer28, and a P-type semiconductor layer 29, the DBR pattern 31 b is formedby alternately laminating two or more insulation layers having differentindexes of refraction in multiple layer on the P-type semiconductorlayer 29, followed by etching the laminated insulating layers accordingto a predetermined pattern via photolithography.

Then, a reflective metal layer 31 a is formed so as to cover the P-typesemiconductor layer 29 and the DBR pattern 31 b, thereby realizing theDBR pattern 31 b that is formed in the reflective metal layer 31 a.

The DBR pattern 31 b improves a bonding force between the P-typesemiconductor layer 29 and the reflective metal layer 31 a whilecompensating for the optical reflection of the reflective metal layer 31a. The DBR pattern 31 b provides a higher bonding force with respect tothe p-type semiconductor layer 29 than the reflective metal layer 31 a.Accordingly, when bonding the p-type semiconductor layer 29 to thereflective metal layer 31 a with the DBR pattern 31 b interposedtherebetween, the bonding force between the P-type semiconductor layer29 and the reflective metal layer 31 a is increased by the bondingcharacteristics between the reflective metal layer 31 a and the DBRpattern 31 b, as compared to when the p-type semiconductor layer 29 isbonded to the reflective metal layer 31 a without any medium.

FIGS. 10 to 12 are cross-sectional views of light emitting diodesaccording to other embodiments of the present invention. Referring toFIGS. 10 to 12, a plurality of grooves or through-holes are formed at alower or upper portion of a second substrate 51, and filled with a metalto form metal layers 52, 53 and 54. As such, the metal layers 52, 53 and54 are sporadically formed in the substrate 51 so that heat can beeffectively discharged through the metal layers. This process isperformed in the preparation of the substrate before forming the secondbonding metal layer 53 on the second substrate 51. Further, in the caseof forming the grooves at the lower portion of the second substrate 51as shown in FIG. 10, the plurality of grooves may be formed to apredetermined depth in the second substrate 51 that is thicker than thatshown in FIG. 10, and filled with a metallic material, followed bypolishing the lower surface of the second substrate 51 to have the samethickness as that shown in FIG. 10.

FIG. 13 is a cross-sectional view of a light emitting diode according toyet another embodiment of the present invention.

Referring to FIG. 13, plural metal patterns 40 are spaced from eachother on a support substrate 51. The support substrate 51 may comprisesapphire, AlN or GaN. The support substrate 51 is homogeneous with asubstrate that is used for growing semiconductor layers constitutinglight emitting cells 30. In this embodiment, the support substrate 51 isa sapphire substrate serving as an insulation substrate.

The metal pattern 40 may include a reflective metal layer and/or anintermediate metal layer. Here, the intermediate metal layer is a metallayer interposed between the light emitting cells 30 and the supportsubstrate 51, and is functionally or regionally distinguished from thereflective metal layer when realized along with the reflective metallayer. However, when not including a separate reflective metal layer,the metal pattern 40 may be realized to have the function of thereflective metal layer. The intermediate metal layer may include aprotective metal layer. The protective metal layer can protect thereflective metal layer. The intermediate metal layer may include abonding metal layer for bonding the support substrate 51.

In this embodiment, the metal pattern 40 includes a reflective metallayer 31 a, a protective metal layer 32 a, a first bonding metal layer33 a, and a second bonding metal layer 53 a. However, the presentinvention is not limited to this configuration, and can be modified invarious forms.

The reflective metal layer 31 a is formed of a metallic material havinghigh reflectivity, for example, silver (Ag) or aluminum (Al). Theprotective metal layer 32 a is a diffusion preventing layer, whichprevents metal elements from being diffused into the reflective metallayer 31 a, and can maintain the reflectivity of the reflective metallayer 31 a. The protective metal layer 32 a may be a single layer ormultiple layers, and formed of, for example, Ni, Ti, Ta, Pt, W, Cr, Pd,or the like.

The first and second bonding metal layers 33 a and 53 a are provided forbonding the reflective metal layer 31 a and the support substrate 51,and each may be formed in a single layer or in multiple layers. Thefirst and second bonding metal layers 33 a and 53 a may be formed of Au,Sn or alloys of Au and Sn (for example, 80/20 wt % or 90/10 wt %). Here,in order to enhance contact characteristics, Cr/Au, Ni or Ti may befurther used. Additionally, the first and second bonding metal layers 33a and 53 a may be formed using In, Ag or Al.

The light emitting cell 30 is located on at least some regions of eachmetal pattern. The light emitting cell 30 includes a lower P-typesemiconductor layer 29 a, an active layer 27 a, and an upper N-typesemiconductor layer 25 a. The active layer 27 a is interposed betweenthe P-type semiconductor layer 29 a and the N-type semiconductor layer25 a, the locations of which can be changed.

The N-type semiconductor layer 25 a may be formed of N-typeAl_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1), and may include an N-type cladlayer. Further, the P-type semiconductor layer 29 a may be formed ofP-type Al_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1), and may include a P-typeclad layer. The N-type semiconductor layer 25 a may be formed by dopingsilicon (Si), and the P-type semiconductor layer 29 a may be formed bydoping zinc (Zn) or magnesium (Mg).

The active layer 27 a serves as a region where electrons and holes arecombined, and comprises InGaN. The wavelength of light emitted from thelight emitting cell is determined according to the kind of materialsconstituting the active layer 27 a. The active layer 27 a may bemultiple layers formed by alternately laminating a quantum well layerand a barrier layer. The quantum well layer and the barrier layer may bebinary to quaternary-compound semiconductor layers represented bygeneral formula Al_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1).

On the other hand, metal wires 57 and 59 are formed to electricallyconnect the N-type semiconductor 25 a to the metal patterns 40 adjacentthereto. For this purpose, an electrode pad 55 may be formed on eachN-type semiconductor 25 a. The electrode pad 55 reduces contactresistance through ohmic contact with the N-type semiconductor layer 25a. Accordingly, the metal wire 57 connects the light emitting cells 30to each other by connecting the electrode pad 55 to the reflective metallayer 31 a as shown in the drawing. The light emitting cells 30connected by the metal wires 57 constitute an array of light emittingcells connected in series. Two or more arrays of light emitting cellsconnected in series can be formed on the substrate 51, and can beconnected anti-parallel to each other to be driven by alternatingcurrent.

FIG. 14 is a cross-sectional view of a light emitting diode according toyet another embodiment of the present invention.

Referring to FIG. 14, a metal pattern 40 is located on a supportsubstrate 51. The support substrate 51 may comprise sapphire, AlN orGaN. The support substrate 51 is homogeneous with a sacrificialsubstrate that is used for growing semiconductor layers constituting alight emitting cell 30. In this embodiment, the support substrate 51 isa sapphire substrate serving as an insulation substrate.

The metal pattern 40 may include a reflective metal layer on at leastsome region of a lower surface of the P-type semiconductor layer 29 a,and an intermediate metal layer covering the reflective metal layer.Here, the intermediate metal layer is a metal layer interposed betweenthe light emitting cell 30 and the support substrate 51 to cover thereflective metal layer between the light emitting cell 30 and thesupport layer 51. The intermediate metal layer may include a protectivemetal layer. The protective metal layer can protect the reflective metallayer. The protective metal layer may be formed in a single layer ormultiple layers. The intermediate metal layer may include a bondingmetal layer that is formed in a single layer or multiple layers forbonding the support substrate 51.

In this embodiment, the metal pattern 40 includes a reflective metallayer 31, a protective metal layer 32 a, a first bonding metal layer 33a, and a second bonding metal layer 53 a. However, the present inventionis not limited to this configuration, and can be modified in variousforms.

The reflective metal layer 31 is formed of a metallic material havinghigh reflectivity, for example, silver (Ag) or aluminum (Al). Theprotective metal layer 32 a is a diffusion preventing layer, whichprevents metal elements from being diffused into the reflective metallayer 31, and can maintain the reflectivity of the reflective metallayer 31. The protective metal layer 32 a may be a single layer ormultiple layers, and formed of, for example, Ni, Ti, Ta, Pt, W, Cr, Pd,or the like.

The first and second bonding metal layers 33 a and 53 a are provided forbonding the reflective metal layer 31 and the support substrate 51, andeach may be formed in a single layer or in multiple layers. The firstand second bonding metal layers 33 a and 53 a may be formed of Au, Sn oralloys of Au and Sn (for example, 80/20 wt % or 90/10 wt %). Here, inorder to enhance contact characteristics, Cr/Au, Ni or Ti may be furtherused. Additionally, the first and second bonding metal layers 33 a and53 a may be formed using In, Ag or Al.

The light emitting cell 30 is located on at least some regions of eachmetal pattern. The light emitting cell 30 includes a lower P-typesemiconductor layer 29 a, an active layer 27 a, and an upper N-typesemiconductor layer 25 a. The active layer 27 a is interposed betweenthe P-type semiconductor layer 29 a and the N-type semiconductor layer25 a, the locations of which can be changed.

The N-type semiconductor layer 25 a may be formed of N-typeAl_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1), and may include an N-type cladlayer. Further, the P-type semiconductor layer 29 a may be formed ofP-type Al_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1), and may include a P-typeclad layer. The N-type semiconductor layer 25 a may be formed by dopingsilicon (Si), and the P-type semiconductor layer 29 a may be formed bydoping zinc (Zn) or magnesium (Mg).

The active layer 27 a serves as a region where electrons and holes arecombined, and comprises InGaN. The wavelength of light emitted from thelight emitting cell is determined according to the kind of materialsconstituting the active layer 27 a. The active layer 27 a may bemultiple layers formed by alternately laminating a quantum well layerand a barrier layer. The quantum well layer and the barrier layer may bebinary to quaternary-compound semiconductor layers represented bygeneral formula Al_(x)In_(y)Ga_(1-x-y)N (0≦x,y,x+y≦1).

A metal wire 57 is formed to supply electric power to the metal pattern40, and a metal wire 59 is formed to supply electric power to the N-typesemiconductor layer 25 a. For this purpose, an electrode pad 55 may beformed on each N-type semiconductor layer 25 a. The electrode pad 55reduces contact resistance through ohmic contact with the N-typesemiconductor layer 25 a.

FIGS. 15 to 20 are cross-sectional view illustrating a method offabricating a light emitting diode shown in FIG. 14.

Referring to FIG. 15, semiconductor layers including a buffer layer 23,an N-type semiconductor layer 25, an active layer 27 and a P-typesemiconductor layer 29 are formed on a first substrate 21, followed byforming reflective metal layers 31 separated from each other on thesemiconductor layers.

Advantageously, the first substrate 21 is transparent like a sapphiresubstrate and coherent to lattices of the semiconductor layers.

The buffer layer 23 and the semiconductor layers 25, 27 and 29 may beformed by metal organic chemical vapor deposition (MOCVD), molecularbeam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or the like.Further, the semiconductor layers 25, 27 and 29 may be consecutivelyformed in a single chamber.

The buffer layer 23 may be formed of a particular material so long as itcan release lattice mismatch between the first substrate 21 and thesemiconductor layers 25, 27 and 29. For example, the buffer layer 23 maybe formed of un-doped GaN.

The reflective metal layer 31 is formed of a metal, preferably, a metalwith high reflectivity, for example Ag, Al, an Ag alloy or an Al alloy,which forms ohmic-contact with the P-type semiconductor layer 29.Further, the reflective metal layer 31 is preferably formed of a metalwith a high heat transfer rate, for example, Au, or a laminate of Au andSn. The reflective metal layer 31 may be formed by plating or depositionvia, for example, a lift-off process.

Referring to FIG. 16, a protective metal layer 32 is formed on theP-type semiconductor layer 29 and the reflective metal layer 31. Theprotective metal layer 32 is formed to cover the reflective metal layer31, and serves as a diffusion preventing layer. A first bonding metallayer 33 is formed on the protective metal layer 32. The first bondingmetal layer 33 is provided for metal bonding and is formed, but is notlimited to, of Au or a laminate of Au and Sn.

Referring to FIG. 17, a second bonding metal layer 53 is formed on asecond substrate 51 separate from the first substrate 21. The secondsubstrate 51 is homogeneous with the first substrate 21.

The second bonding metal layer 53 is provided for metal bonding with thefirst intermediate metal layer 31, and is not limited to a particularmaterial. The second bonding metal layer 53 may be formed of Au, Sn oralloys of Au and Sn (for example, 80/20 wt % or 90/10 wt %) in a singlelayer or multiple layers. Here, in order to enhance contactcharacteristics, Cr/Au, Ni or Ti may be further used. Additionally, thesecond bonding metal layer 53 a may further comprise In, Ag or Al.

Referring to FIG. 18, the first bonding metal layer 33 and the secondbonding metal layer 53 are bonded to each other to face each other. Suchbonding can be easily performed through application of a predeterminedpressure and/or heat. Then, a laser is irradiated from a side of thefirst substrate 21. The laser may be, for example, a KrF (248 nm) laser.Since the first substrate 21 is a transparent substrate like a sapphiresubstrate, the laser passes through the first substrate 21 and isabsorbed by the buffer layer 23. As a result, the buffer layer 23 isdecomposed at an interface between the buffer layer 23 and the firstsubstrate 21 by the absorbed radiation energy, so that the substrate 21is separated from the semiconductor layers.

Referring to FIG. 19, after the first substrate 21 is separated from thesemiconductor layers, the remaining buffer layer 23 is removed to exposethe surface of the N-type semiconductor layer 25. The buffer layer 23can be removed by etching or polishing.

Referring to FIG. 20, the semiconductor layers 25, 27 and 29, and themetal layers 31, 32, 33 and 53 are patterned by photolithography oretching to form metal patterns separated from each other and a lightemitting cell 30 located on some regions of each metal pattern.

The light emitting cell 30 includes the P-type semiconductor layer 29 a,the active layer 27 a, and the N-type semiconductor layer 25 a, whichare subjected to the patterning process. The semiconductor layers 25 a,27 a and 29 a may be patterned to have identical shapes.

On the other hand, since the second substrate 51 is an insulationsubstrate and the metal patterns 40 are separated from each other, thelight emitting cells 30 are electrically isolated from each other.

With the light emitting cells 30 electrically isolated from each other,the second substrate 51 is divided into individual chips by dicing thesecond substrate 51 for the respective light emitting cells 30. Then,metal wires 57 and 59 are formed on the respective upper surfaces of thelight emitting cell 30 and the metal pattern 40, thereby providing alight emitting diode as shown in FIG. 14.

On the other hand, before forming the metal wires, an electrode pad 55may be formed on the N-type semiconductor layer 25 a. The electrode pad55 forms ohmic-contact with the N-type semiconductor layer 25 a. Here,although the metal wire 57 is shown as being connected to a right upperside of the metal pattern in the drawing, the metal wire 57 can beconnected to a left upper side thereof, as needed.

In this embodiment, since the metal pattern 40 is formed, it is possibleto eliminate a process of forming a separate electrode pad on the P-typesemiconductor layer 29 a.

On the other hand, according to this embodiment, the P-typesemiconductor layer 29 and the N-type semiconductor layer 25 may beformed in a reverse order. In this case, a transparent electrode may beformed on the P-type semiconductor layer 29 after removing the bufferlayer 23.

According to another embodiment of the invention, instead of dicing thesecond substrate 51 for the respective light emitting cells 30 to dividethe second substrate 51 into individual chips with the light emittingcells 30 electrically isolated from each other, the N-type semiconductorlayer 25 a may be electrically connected to the metal patterns 40adjacent to the N-type semiconductor layer 25 a via the metal wires 57and 59. The light emitting cells 30 connected by the metal wires 57constitute an array of light emitting cells connected in series. Two ormore arrays of light emitting cells connected in series can be formed onthe substrate 51, and can be connected anti-parallel to each other to bedriven by alternating current.

FIG. 21 is a cross-sectional view of a light emitting diode according toyet another embodiment of the present invention.

Referring to FIG. 21, the configuration and operation of the lightemitting diode according to this embodiment are similar to those of thelight emitting diode illustrated in FIG. 14. However, the light emittingdiode of this embodiment has an indium tin oxide (ITO) layer 31 cbetween a lower surface of the P-type semiconductor layer 29 a and thereflective metal layer 31.

The ITO layer 31 c may function as an ohmic contact layer with respectto the P-type semiconductor layer 29 a and the reflective metal layer31. Accordingly, the ITO layer 31 c can enhance luminescencecharacteristics by improving the ohmic characteristics between theP-type semiconductor layer 29 a and the reflective metal layer 31.

Although the present invention has been described with reference to theembodiments, this invention is not limited to the embodiments, andvarious modifications and changes can be made by a person havingordinary knowledge in the art without departing from the scope andspirit of the invention as defined by the accompanying claims.

Further, although the metal wire connecting the light emitting cells isillustrated as having an air-bridge shape in the embodiments of theinvention, it can be realized in any shape through a step-cover process.

What is claimed is:
 1. A method of fabricating a light emitting diode,the method comprising: forming semiconductor layers on a firstsubstrate, the semiconductor layers comprising a buffer layer, a firstconductive type semiconductor layer, an active layer, and a secondconductive type semiconductor layer; forming a metal pattern on thesecond conductive type semiconductor layer; forming a bonding metallayer on a second substrate; bonding the metal pattern and the bondingmetal layer; separating the first substrate from the semiconductorlayers; patterning the semiconductor layers, the metal pattern, and thebonding metal layer to form separated metal patterns and light emittingcells arranged on at least one region of the respective separated metalpatterns; and dicing the second substrate to form individual lightemitting diode chips, wherein the second substrate is homogeneous withthe first substrate, and wherein the separating of the first substratefrom the semiconductor layers comprises irradiating light onto a side ofthe first substrate to decompose the buffer layer formed on an oppositeside of the first substrate.
 2. The method of claim 1, wherein the firstsubstrate and the second substrate comprise sapphire.
 3. The method ofclaim 1, wherein forming the metal pattern comprises: forming aplurality of reflective metal layers separated from each other on thesecond conductive type semiconductor layer; and forming an intermediatemetal layer covering the second conductive type semiconductor layer andthe reflective metal layers.
 4. The method of claim 1, furthercomprising: forming a plurality of grooves or through-holes in an upperportion or a lower portion of the second substrate, and forming metallayers in the grooves or the through-holes, before forming the bondingmetal layer on the second substrate.
 5. A method of fabricating a lightemitting diode, the method comprising: forming semiconductor layers on afirst substrate, the semiconductor layers comprising a buffer layer, afirst conductive type semiconductor layer, an active layer, and a secondtype conductive semiconductor layer; forming a metal pattern on thesecond conductive type semiconductor layer; forming a bonding metallayer on a second substrate; bonding the metal pattern and the bondingmetal layer; separating the first substrate from the semiconductorlayers; patterning the semiconductor layers, the metal pattern, and thebonding metal layer to form separated metal patterns and light emittingcells arranged on at least one region of the respective separated metalpatterns; and forming a metal wire to electrically connect an uppersurface of a first light emitting cell to the metal pattern adjacent toand spaced apart from the upper surface thereof, wherein the secondsubstrate is homogeneous with the first substrate, and wherein theseparating of the first substrate from the semiconductor layerscomprises irradiating light onto a side of the first substrate todecompose the buffer layer formed an opposite side of the firstsubstrate.
 6. The method of claim 5, wherein the first substrate and thesecond substrate comprise sapphire.
 7. The method of claim 5, whereinforming the metal pattern comprises: forming a plurality of reflectivemetal layers separated from each other on the second conductivesemiconductor layer; and forming an intermediate metal layer coveringthe second conductive semiconductor layer and the reflective metallayers.